This invention relates to a heat shield for a combustion chamber, particularly for an annular combustion chamber of a gas turbine, having a through-hole for a burner. The rearward side of the heat shield which faces away from the combustion chamber is acted upon by cooling air. The heat shield has a web extending around on the edge of the through-hole. Concerning the known state of the art, reference is made to U.S. Pat. No. 5,307,637 in which case the web is used for receiving or bearing the burner.
As known, the heat shield provided in the head of a combustion chamber is used for protecting the head area of the combustion chamber, which is constructed in the manner of a dome, or the front panel provided therein from the effect of the hot gas situated in the combustion chamber as well as from an excessive heat radiation. In order to be able to carry out this function, the heat shield itself must be cooled. For this purpose, conventional heat shields have so-called effusion holes in the surface facing the combustion chamber by way of which cooling air can flow through from the rearward side in order to place a cooling air film on the hot surface of the heat shield. This is explained in detail in U.S. Pat. No. 5,307,637. Another known heat shield arrangement is indicated in European Patent document EP-A-0 521 687, in which case air passage openings are provided in a web-type section, by which air passage openings cooling air can arrive in the combustion chamber.
However, since it is not always possible to sufficiently cool all endangered zones of the heat shield according to this known state of the art, the invention has the object of indicating further measures by which an improved heat shield cooling can be achieved.
The achieving of this object is characterized in that the web has a plurality of air passage holes which are inclined at an angle with respect to the direction pointing into the center of the through-hole such that an air flow entering through the air passage openings into a ring-shaped channel between the heat shield and the burner, and arriving from there in the combustion chamber, forms a swirl which has the same direction as the swirl which is formed by the combustion air supplied by way of the burner and which has a swirl axis extending perpendicularly to the surface of the heat shield. Advantageous embodiments and further developments are described herein.
The invention will be explained in detail by means of a preferred embodiment.